Three layer grinding wheel

ABSTRACT

A multilayer circular grinding wheel includes at least three substantially planar layers including an inner layer and two outer layers immediately adjacent to the inner layer, of which at least the inner layer has a proportion of diamond abrasive grit, the proportion of diamond in the abrasive grit being greater in the inner layer than in the outer layers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to German Patent Application No. 102019122711.9 filed on Aug. 23, 2019 and is a Continuation Application of PCT Application No. PCT/EP2020/073533 filed on Aug. 21, 2020. The entire contents of each application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a grinding wheel and to a use of such a grinding wheel.

2. Description of the Related Art

Grinding wheels consisting of a single homogeneous layer of abrasive material are generally known. For example, WO 2006/079444 A1 shows a grinding wheel with a homogeneous layer of diamond-containing abrasive grain in a synthetic resin bond for grinding ceramic balls. The grinding wheel is acted upon in the axial direction, and the balls to be ground run in grooves aligned concentrically to the axis of rotation.

Multi-layer grinding wheels are also known, for example from the document JP 2003300166 A, which discloses a grinding wheel with three layers arranged on top of each other in a sandwich-like manner in the axial direction is described. The grinding wheel is part of a grinding device for precise cuts in the radial direction. Particularly good dimensional accuracy is to be achieved in that a middle layer with relatively coarse abrasive grit is made of diamond, while the two axially adjacent outer layers are made of abrasive grit of diamond with a finer grain size. In use, wear of the two outer layers causes the grinding peripheral surface of the wheel to become convex so that the wheel centers itself in the workpiece. Further, CN106944938 discloses a three-layer grinding wheel in which the two outer layers contain a proportion of diamond abrasive grit, while the middle or inner layer contains alumina and synthetic resin. This design improves heat dissipation through the inner layer of the grinding wheel.

Grinding wheels with a matrix containing homogeneous or equal amounts of diamond abrasive grit in all layers are expensive to manufacture. A three-layer grinding wheel with a middle or inner layer free of diamond abrasive grit is not suitable for grinding ceramic balls.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide grinding wheels each including at least three layers, is less expensive to manufacture than the prior art, and is particularly suitable for grinding ceramic balls.

Because a grinding wheel according to a preferred embodiment of the present invention is provided with an inner or middle layer and at least two outer layers, and the inner layer has a higher proportion of diamond in the abrasive grit than the two outer layers immediately adjacent to the inner layer, it is possible to save on diamond abrasive grit compared with grinding wheels with homogeneous construction or grinding wheels with layers that differ only in grit size but not in diamond content. In addition, such a grinding wheel can be used advantageously for grinding ceramic balls, since the guide grooves are quickly formed in the outer layer coming into contact with the balls, and the inner layer acts predominantly or exclusively abrasively, i.e., to perform the actual grinding process.

Advantageously, at least the inner layer is designed with abrasive grain in a synthetic resin bond. It is further advantageous if the two outer layers directly adjacent to the inner layer on a respective surface side of the inner layer have the same abrasive grain, and in particular, it is further advantageous that these two outer layers have the same thickness or substantially the same thickness in the axial direction.

When used for ball grinding, the new grinding wheel is preferably bonded with one outer plane side to a metallic backing plate. The outer layer lying directly on the backing plate is then not used for grinding or guiding purposes during ball grinding. However, it has proved advantageous to provide this layer opposite to the other outer layer, which is of identical design, since this reduces or minimizes distortion of the entire grinding wheel and in particular of the inner layer during production.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of preferred embodiments of the present invention are described below with reference to the drawings.

FIG. 1 shows a section of a three-layer grinding wheel in a view in the radial direction.

FIG. 2 shows the grinding wheel of FIG. 1 with prepared guide grooves for use in ball grinding.

FIG. 3 shows the grinding wheel from FIG. 1 and FIG. 2 in its use for ball grinding in a corresponding device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a grinding wheel 1 according to a preferred embodiment of the present invention is schematically illustrated in a cross-section in broken-off form. The grinding wheel 1 includes an inner layer 2, which is sandwiched between a first outer layer 3 and a second outer layer 4. The inner layer 2 has a higher proportion of diamond in the abrasive grain than the two outer layers 3 and 4. For example, the inner layer 2 may have a proportion of 50% by weight (wt%), 75% by weight or even 90% by weight of diamond in the abrasive grain. This specification is the proportion in the abrasive grain without the bond matrix. In a preferred embodiment, the abrasive grain may also consist of 100% diamond. The grit size of the abrasive grain is not essential to preferred embodiments of the present invention. Suitable grit sizes are known from the prior art.

The two outer layers 3 and 4 have the same or essentially the same structure. They also contain abrasive grit, but with a lower or no diamond content. Thus, the content of diamond in these two layers may be less than 50% by weight, in particular less than 25% and even less than 10%. In a preferred embodiment, the two outer layers 3 and 4 are essentially free of diamond abrasive grain, i.e., except for impurities or traces unavoidable in the manufacturing process.

If the inner layer 2 is not manufactured with 100% of diamond abrasive grit, the required total of 100% can be supplemented with less expensive abrasive grit such as corundum (Al₂O₃), in particular high-grade corundum, silicon carbide (SiC), but also any other known abrasive grit. The two outer layers also contain conventional abrasive grit. In particular, in the preferred embodiment in which the two outer layers 3 and 4 are free of diamond abrasive grit, all of the abrasive grit is selected from lower cost material such as corundum, SiC, another abrasive grit, or a mixture of the eligible non-diamond abrasive grits.

The inner layer 2 and the outer layers 3 and 4 are produced by hot pressing in a synthetic resin bond. The ratio between abrasive grit and synthetic resin is suitably selected, as is common in the prior art. The pore volume of an abrasive wheel according to a preferred embodiment of the present invention is preferably between 3 and 10%.

The essentially identical structure of the two outer layers 3 and 4 ensures that the grinding wheel practically does not warp during or after manufacture, for example, in the cooling phase. In the case of a grinding wheel with an outer layer applied on only one side, warpage is to be expected due to different heat conduction and heat capacity as well as due to different thermal expansion of the materials.

The grinding wheel is a circular wheel, which is rotationally symmetrical to an axis D.

The thickness in the direction of the axis D can be selected depending on the application. Thus, the dimensions of the wheel and of the individual layers 2, 3 and 4 are selectable and dependent on the application situation. The wheel diameter can also be selected and adapted to the needs of the grinding machine. In particular, the thickness of the outer layers 3 and 4 can be smaller than the thickness of the inner layer 2, as these mainly serve to stabilize the grinding wheel. Layer 3, which serves as the infeed layer for the ceramic balls, is ground down after hot pressing to a dimension appropriate for the application, i.e., for the ball diameters to be ground in use.

FIG. 2 shows the grinding wheel 1 from FIG. 1 in a likewise cut, broken-off representation. Here it can be seen in cross-section that, compared with the initial situation in FIG. 1, the upper outer layer 3 is subsequently (after hot pressing) provided with guide grooves 5, which prepare the grinding wheel 1 for use in ball grinding. The guide grooves 5 are concentric, circular circumferential grooves which are arranged in the outer surface of the outer layer 3 and which are symmetrically and concentrically aligned with respect to the axis of rotation D.

FIG. 3 illustrates the use of the grinding wheel 1 according to a preferred embodiment of the present invention for ball grinding on a machine with a vertical drive axis. FIG. 3 shows in a schematic representation the device for ball grinding in a side view. Here, a stationary guide disc 1 is provided, preferably made of cast steel. The guide disk 10 has circumferential guide grooves 11 on its underside, in which a plurality of balls 12 to be ground are guided. From the underside, a backing plate 13 is provided with the grinding wheel 1 arranged thereon with the inner layer 2 and the two outer layers 3 and 4, which is to be set in rotation by a drive shaft 15.

For grinding, a pressure P is exerted on the stationary guide disk 10 from the upper side. The backing plate 13 is set in rotation by a drive, so that the balls 12 roll in the guide grooves 11 and in particular also in the guide grooves 5 of the grinding wheel 1. While the guide grooves in the first outer layer 3 do not yet make any appreciable contribution to the ablation of ceramic balls, the effective grinding process begins when the balls 12 have worked their way through the layer 3 and come into contact with the diamond-containing layer 2. The speed differences in the different areas of the guide grooves cause the abrasive grain to move relative to the surface of the ceramic ball. The abrasive grain then causes an abrasion of the surface of the ball and thus an improvement of the surface quality and the ball shape.

A grinding wheel according to a preferred embodiment of the present invention can be used on a ball grinding machine with a vertical drive shaft as well as on a ball grinding machine with a horizontal drive shaft.

An advantage of the grinding wheel described in this respect, especially when used for ball grinding, is that the entire thickness of the inner layer 2 can be used for the grinding process. The outer layers, which are manufactured with less expensive abrasive grit, serve only for the initial guidance of the ball blanks in the guide groove 5 and to fasten the grinding wheel on the backing plate 13. The supporting layer 4 has the further effect that the grinding diamond-containing layer 3 can be used up to the breakthrough and, in contrast to single-layer discs, a reduction of the diamond material to be discarded is thus achieved. If both tasks were performed by the diamond layer in the case of a single-layer diamond grinding wheel, the overall consumption of diamond abrasive grain is higher than in the case of the multilayer grinding wheel shown above with an inner layer containing a higher proportion of diamond. Furthermore, the softer running-in layer 2 leads to the fact that the process of groove formation on the one hand takes place significantly faster than in the hard diamond layer and on the other hand the number of ball batches with low quality is reduced.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A multilayer circular grinding wheel comprising: at least three substantially planar layers including an inner layer and two outer layers immediately adjacent to the inner layer, of which at least the inner layer has a proportion of diamond abrasive grit such that the proportion of diamond in the abrasive grit is greater in the inner layer than in the outer layers.
 2. The grinding wheel according to claim 1, wherein the inner layer has a proportion of at least 50% by weight of diamond in the abrasive grain.
 3. The grinding wheel according to claim 1, wherein the inner layer has a proportion of at least 75% by weight of diamond in the abrasive grain.
 4. The grinding wheel according to claim 1, wherein the inner layer has a proportion of at least 90% by weight of diamond in the abrasive grain.
 5. The grinding wheel according to claim 1, wherein the outer layers each have a proportion of less than 90% by weight diamond in the abrasive grain.
 6. The grinding wheel according to claim 1, wherein the outer layers each have a proportion of less than 75% by weight diamond in the abrasive grain.
 7. The grinding wheel according to claim 1, wherein the outer layers each have a proportion of less than 50% by weight of diamond in the abrasive grain.
 8. The grinding wheel according to claim 1, wherein the grinding wheel includes exactly three layers including abrasive grains.
 9. The grinding wheel according to claim 1, wherein the outer layers have a same structure or substantially a same structure, and a same axial thickness or substantially a same axial thickness.
 10. The grinding wheel according to claim 1, wherein the inner layer and the outer layers are made of a synthetic resin bond.
 11. A method of using the grinding wheel according to claim
 1. 12. The method according to claim 11, wherein the grinding wheel is bonded with an outer side to a metallic support plate. 